What is the medication for itchy rashes turning black on multiple parts of the body?

Hi, my wife was prescribed Radiance-H capsules by my dermotologist. She has had 4 tablets so far, and, there have been rashes on multiple parts of the body. On left leg below the knee, and, on the rear. These rashes itch a lot, and, have turned dark red in color over the past day. The skin has become hard and is swollen like a severe allergy. In fact, these are not going away even though she has stopped the capsules for the past couple of days. She also took allegra 180 initially thinking it was an allergic reaction (3 tablets over 3 days, one per day). But, no appreciable difference. What would you prescribe to bring down the allergy and what solution for stopping the itching.